1. Field of the Present Invention
The present invention relates to a power supply unit using a nonaqueous electrolyte secondary battery as its power source and an electric apparatus to which power is supplied from the power supply unit.
2. Description of the Background Art
Along with reduction in size and weight of portable electronic devices, there is an increasing demand recently for light-weight high-energy density nonaqueous electrolyte secondary batteries. The battery has the advantages described above, but, because the electrolyte solution contains a relatively degradable organic solvent, the electrolyte solution may decompose on the positive electrode surface if the battery is left in the fully charged state at high temperature, generating gas, increasing the internal pressure, and possible leading to drastic deterioration in its capacity.
It would be effective to reduce the charge depth (hereinafter, referred to SOC) of nonaqueous electrolyte secondary battery by discharge, for prevention of such troubles. The charge depth, a relative value between 100% at during full charge and 0% at full discharge, is a rate of the charged capacity relative to the rated battery capacity. However, the SOC level of the nonaqueous electrolyte secondary battery is not determined usually when an electric apparatus containing a nonaqueous electrolyte secondary battery as power source is brought into vehicle, and the electric apparatus is often exposed to high temperature (for example during shipment), leading to increased possibility of the problems above. It would become easier for the third person to determine whether the electric apparatus may or may not be brought into vehicle correctly by showing the state of the nonaqueous electrolyte secondary battery accurately.
For that reason, it would be effective to use a power source system that, when a high-SOC lithium-ion secondary battery is left at high temperature, discharge the battery to an SOC in the safe region while sending a message (see WO 2006/064726 pamphlet).
However, the power source system initiates discharge only when the device is brought into vehicle and exposed actually to high temperature, and thus, it was difficult to show the third person that an electric apparatus having a nonaqueous electrolyte secondary battery as power source does not show drastic decrease in capacity when shipped, before it is bought in vehicle. If the temperature regarded as high temperature in the power source system is set lower for more reliable prevention of drastic decrease in capacity, slight heat generation during charge may be regarded falsely as high temperature, prohibiting effective charging and giving a charged battery extremely lower in practical performance under ambient atmosphere.